Electron discharge apparatus



Oct. 29, 1946. J,H.FREML.IN ETAL 2,410,054-

ELECTRON DI SCHARGE APPARATUS Filed June 2, 1942 INVENTOBS A TIDE/V5) Patented Oct. 29.1946

I 2,410,054, ELECTRON DISCHARGE APPARATUS John Heaver Fremlin and Roger Norman Hall, London W. C. 2, England, assignors to Standard Telephones and Cables Limited, London, England, a British company Application June 2, 1942 Serial No. 445,503 In Great Britain August 2, 1940 This invention relates to electron discharge apparatusemploying electron beams focussed or directed in a straight path by means of a magnetic field. The invention is primarily applicable to apparatus operating at extremely high irequencies, particularly apparatus of electron-velocity modulated type.

Incertain electron tubes for use at very high frequencies, it is necessary to use a magnetic field for directing the electron paths if it is desired to obtain the highest efficiency. This may be done in the case of many sealed off tubes by means of a permanent magnet. In order to do this with as light a magnet as possible the gaps in the magnetic circuit must be made as small as possible. It is proposed, therefore as a first means of doing this that piece of high permeability material should be incorporated in the vacuum tube structure as pole-pieces or extensions of external pole-pieces. Such pole-pieces are also useful in obtaining a concentrated field in the case where an electro-magnet is used.

Developing further the same idea, it is proposed that the vacuum envelope or a part thereof be made itself of a material capable of maintaining a high degree of permanent magnetisation, if necessary plated inside with a metal of high conductivity to avoid high frequency losses.

Alternatively, if it is desired to avoid the use of magnetic materials for the external envelope, the structure including the permanent magnet may be contained in a glass envelope of any desired size, the need for minimum size of envelope being eliminated by the fact that the magnet structure is internal.

In further aspects, the invention resides in electron discharge apparatus of the electron-velocity-modulated type comprising within a vacuum-tight envelope an electron gun adapted to project electrons in a beam through a resonator structure, and, for collecting the electrons, a collector electrode which may form part of the resonator structure, characterised by one of the following features:

(a) Magnetic pole-pieces are provided within the envelope at the ends of the electron beam path, said pole-pieces being adapted to form part of a magnetic circuit including a permanent magnet or an electromagnet outside the envelope.

(b) The envelope itself comprises a permanent magnet having poles at the ends of the beam path for focussing the beam.

A permanent magnet is provided within the envelope and embracing the electron gun 7 Claims. (Cl. 25027.5)

2 and resonator structure to provide a focussing field along the beam path,

Embodiments of the invention as applied to velocity modulated tubes of the kind disclosed in United State Patent No. 2,320,860 to J. Fremlin will now be described with reference to Figs. 1 and 2 of the accompanying drawing.

Fig. 1 is, a perspective view of a tube cut away to show a cross-section along the beam path.

The electrode structurecomprises a co-axial tube resonator I With fins 2, 3 bounding apertures for the beam path. A cathode 4 and a focussing electrode 5 together forming an electron gun are located in line with the apertures in the resonator and are preferably carried on the resonator. These elements are slid into a tubular metal envelope portion or sheath 6 A permanent magnet I is provided outside the sheath 6 to provide an intense field along the beam path. In order to shorten the gap as much as possible and thus obtain a stron field, magnetic pole-pieces 8, 9 are provided inside the sheath.

Pole-piece 8 lies behind the cathode 4 and i insulated by sheet material NJ from the sheath so that a field of the high potential of the resonator and the sheath is not set up in close proximity to the cathode. This pole-piece may if desired be connected to the cathode;

Pole-piece 9 forms a part of the resonator structure and serves also as a collecting electrode. Its sides may be covered with a more highly conductive metallic layer if desired. Its collecting face may be so shaped or coated as to suppress secondary emission if this is required.

It will be seen that a substantial shortening of the magnetic field gap is accomplished by the provision of th internal pole-pieces, and that only a single gap is employed this gap thus shortened still includes the entire length of the beam.

Fig. 2 is a similar view of a modified. tube in which a tubular permanent magnet ll, formed with inwardly-projecting pole-pieces 8' and 9 in lin with the apertures in the resonator ll, constitutes a part of the evacuated envelope itself. The internal surface of the magnet may be plated with a metal of high conductivity.

If it is desired to avoid the use of magnetic materials for the external envelope, the structure including the permanent magnet ll may be contained in a glass envelope as indicated in Fig. 2.

What is claimed is:

1. Electron discharge apparatus of the electron velocity modulated type comprising a tubular metallic member forming part of a vacuum-tight envelope, a resonator comprising a short length of coaxial line having diametric aligned apertures and disposed within said tubular metallic member, means for generating and directing a beam of electrons through said apertures also disposed within said tubular metallic member, and a pair of magnetic pole pieces disposed one at each end of the electron beam path having only a single gap therebetween, one of said pole pieces being mounted upon saidvtubular metallic member and the other of said pole pieces being mounted upon said resonator.

2. Electron discharge apparatus of the electron velocity modulated" type comprising a resonator including a short length of coaxial line having diametric aligned apertures, means adjacent thereto for generating a beam of electrons and positioned for directing it through said apertures, and a single tubular permanent magnet surrounding said resonator and provided with a pair of inwardly directed pole pieces disposed one at each end of the electron beam path and in line with said apertures,

3. An electron discharge apparatus of the electron-velocity modulation type comprising beam generating electrodes within a vacuum-tight envelope, a cavity resonator positioned adjacent to the path of the beam for cooperating with the electron beam, beam focusing means having magnetic pole-pieces located respectively at the ends 4 of the beam path with a single magnetic gap therebetween including the entire length of the beam path, at least one pole-piece having a poleface within the envelope.

4. An electron discharge apparatus according to claim 3 wherein one magnetic pole-piece constitutes a collector electrode and is conductively connected to the resonator.

5. An electron discharge apparatus according to claim 3 wherein there is means for completing a magnetic circuit of the pole-pieces comprising a permanent magnet located within the envelope.

6. An electron discharge apparatus according to claim 3 in which the cavity resonator comprises a short length of coaxial line having diametrical aligned apertures through which the electron beam path passes.

7. An electron discharge apparatus of the electron-velocity modulation type comprising electron beam generating electrodes, a cavity resonator constituted by a short length of coaxial line having diametrical aligned apertures through which the beam path passes, beam focusing means having magnetic pole-pieces located respectively at the ends of the beam path, at least one pole-piece having a pole-face with-in the envelope and forming part of the resonator.

JOHN HEAVER FREMLIN. ROGER NORMAN HALL. 

